We have identified novel mechanisms by which dendritic cells (DCs) influence T helper cells to mount immune responses in the lung. Our studies show that the allergen house dust mite and the Th2-skewing mucosal adjuvant cholera toxin (CT) induce expression of c-kit and its ligand, stem cell factor, on DCs resulting in high level of interleukin-6 (IL-6) production from the DCs promoting Th2/Th17 differentiation but inhibiting Th1 differentiation. DCs lacking functional c-kit were unable to produce IL-6 and induce a robust Th2 or Th17 response and elicited diminished allergic airway inflammation when adoptively transferred into mice. DCs generated from mice expressing a catalytically inactive form of the p1104 subunit (p110D910A) of PI3 kinase secreted lower levels of IL-6 upon stimulation with CT. Along with our investigations of mechanisms underlying DC-mediated T cell differentiation, we have been also pursuing pathways that might contribute to DC-mediated tolerance to inhaled antigens. In these studies, we have the unexpected finding that lack of the enzyme indoleamine 2,3 dioxygenase (IDO) in mice does not impair antigen-induced airway tolerance although IDO has been associated with immune suppression in most studies. In contrast, mice lacking IDO displayed an attenuated allergic phenotype. Myeloid dendritic cells isolated from lung-draining lymph nodes of mice immunized for either Th1 or Th2 response revealed fewer mature DCs in the LNs of IDO-/- mice. However, the net functional impact of IDO deficiency on antigen-induced responses was more remarkable in the Th2 model than in the Th1 model. Our overall hypothesis for this renewal application is that DC-mediated T cell differentiation in the lung-draining lymph node in response to allergens or pathogens is orchestrated by: I. Expression of cell surface molecules such as c-kit and additional mediators (IDO and PGE2) in DCs, which, in turn, 2. Regulate signaling pathways such as PI3 kinase/Akt and MAPK to influence a) the balance of the downstream cytokines IL-6 and IL-12 and/or b) cell surface molecules such as Notch ligands in DCs that together influence the immune response. To address this hypothesis we will: Aim I. Characterize pathways in DCs downstream of c-kit that differentially promote expression of IL-6 and Notch ligand, Jagged-2, but downregulate IL-12 production. Aim II. Generate c-kit W42 mutant mice in a CD11c-expressing cell-specific fashion and effects on T cell responses in different models of lung inflammation. Aim III. Characterize defects in lung DC function in the absence of IDO. PUBLIC HEALTH RELEVANCE: Dendritic cells (DCs) play an essential role in guiding immune responses in the lung in response to allergens and infectious agents. In our efforts to understand the mechanisms of this process, we have identified molecules expressed by DCs that play decisive roles in the outcome of an immune response. Our goal in this application is to understand in detail the events orchestrated by molecules secreted (cytokines), expressed within (the enzyme indoleamine 2, 3 dioxygenase) or on the cell surface (c-kit and stem cell factor) of DCs during response to allergens and pathogens in the lung. These studies will help identify targets for inhibiting undesired immune responses in the lung at the same time promoting those that protect from infectious agents.